Monitoring a mobile device

ABSTRACT

Devices, systems, and methods for monitoring traffic, such as vehicle traffic on a roadway, using identification information acquired using a Bluetooth protocol. A sensor is configured to scan for discoverable Bluetooth devices within a flow of vehicle traffic and to create a log of identified Bluetooth devices. A system includes multiple sensors at known locations along a route and is operable to identify a Bluetooth device identified at multiple sensors.

RELATED APPLICATIONS

This application is a continuation (and claims the benefit of priorityunder 35 USC 120) of U.S. application Ser. No. 13/609,440 filed Sep. 11,2012, which is a divisional of U.S. application Ser. No. 12/348,661,filed Jan. 5, 2009, now U.S. Pat. No. 8,280,617, issued Oct. 2, 2012,which claims the benefit to U.S. Provisional Patent Applications, eachof which is incorporated herein in its entirety: Ser. No. 61/018,724filed Jan. 3, 2008, and titled “Anonymous Bluetooth Traffic Monitoring”,Ser. No. 61/026,565 filed Feb. 6, 2008, and titled “Anonymous BluetoothTraffic Monitoring”, and Ser. No. 61/060,304 filed Jun. 10, 2008, andtitled “Anonymous Bluetooth Traffic Monitoring”.

TECHNICAL FIELD

This disclosure relates to monitoring mobile devices, for example, tofacilitate vehicle traffic monitoring.

BACKGROUND

Vehicle traffic monitoring typically involves collecting traffic datafrom vehicles traveling on a road and analyzing the collected trafficdata to learn about vehicle traffic patterns. For example, vehiclestraveling past a data acquisition site may be counted for use indetermining a total traffic flow volume at the data acquisition siteduring the period of counting. Additionally, or alternatively,instantaneous speed of vehicles may be monitored to determine trafficflow speed. Each such analysis typically involves aggregating theinformation collected, for example, from a selected geographic area ortime, and processing the aggregated information, such as by averaging,to generate measures of traffic flow. These measures are then used, forexample, to predict traffic patterns, or to evaluate the adequacy oftraffic infrastructure. For example, a count of vehicles travelingthrough a selected intersection may be used to determine whether atraffic control device is needed at the intersection, and if so, whattype of traffic control device.

Vehicle traffic data collection for use in vehicle traffic analysis isan integral part of a traffic monitoring process, because withoutadequate and reliable data, no valid conclusions may be obtained. Toenable data collection, permanently installed sensor devices andsystems, including those embedded in the roadway, have been implementedto detect vehicle traffic on the roadway at the location of the sensordevice. Existing devices installed for other purposes, such as cellphone transceiver devices and toll collection devices installed alongroadways, also have been used to collect data of vehicle traffic, ashave portable sensor devices.

SUMMARY

In one aspect, a computer-implemented process of monitoring vehicletraffic along a roadway includes a first sensor disposed at a firstlocation along a roadway that initiates a first inquiry scan accordingto a Bluetooth standard, receives a first inquiry response including afirst device identifier that identifies a mobile device according to aBluetooth standard from the mobile device at a first time, stores thefirst identifier received in the first inquiry response, stores a firstsensor identifier that identifies the first sensor, and associates thefirst device identifier with the first sensor identifier and a firsttime stamp that reflects the first time. A second sensor that isdisposed at a second location along the roadway initiates a secondinquiry scan according to a Bluetooth standard, receives a secondinquiry response including the first device identifier according to aBluetooth standard at a second time, stores the first device identifier,stores a second sensor identifier that identifies the second sensor, andassociates the first device identifier with the second sensor identifierand a second time stamp that reflects the second time. The first deviceidentifier is identified as being associated with the first sensoridentifier and with the second sensor identifier, and, based on theidentification that the first device identifier is associated with thefirst sensor identifier and the first time stamp as well as with thesecond sensor identifier and the second time stamp, at least one vehicletraffic statistic is derived based on the first time stamp, the secondtime stamp, the first location, and the second location.

The process may include one or more additional features. For example,the first identifier may be a MAC address of the first sensor and thesecond identifier may be the MAC address of the second sensor. The atleast one vehicle traffic statistic may be an average vehicle speedbetween the first location and the second location. The first inquiryscan may include an inquiry scan routine, and the inquiry scan routinemay comprise an interlaced inquiry scan routine. The inquiry scanroutine may be configured to terminate when a number of responsesreceived equals a threshold number or after completing a maximum numberof iterations of the inquiry scan routine. One or more parameter of theinquiry scan routine may be adjusted, for example, by changing thethreshold number of responses and/or the maximum number of iterations.The association of the first device identifier with the first sensoridentifier and the first time and/or the association of first deviceidentifier with the second sensor identifier and the second time mayindicate that the mobile device was located at the first location at thefirst time, and/or was located at the second location at the secondtime. The first location may be derived from a global positioningsatellite (GPS) communication. The first inquiry response may furtherinclude clock information of the mobile device, and page scan typeinformation, one or both of which may be discarded before transmitting aname discovery request. The first sensor may initiate a third inquiryscan before transmitting a name discovery request. A route distancebetween the first location and the second location may be determined,and the at least one vehicle traffic statistic may be based on the routedistance.

In another aspect, a computer-implemented process may include a firstsensor receiving a first inquiry response according to a Bluetoothstandard including a device identifier that identifies a mobile devicein response to a first inquiry scan of the first sensor, associatinginformation of the first sensor with the device identifier, a secondsensor receiving a second inquiry response according to a Bluetoothstandard including the device identifier in response to the secondinquiry scan, and determining at least one vehicle traffic statisticbased on a comparison of the information of the first sensor associatedwith the device identifier and the information of the second sensorassociated with the device identifier.

The process may include one or more additional features. For example,the at least one vehicle traffic statistic may be a travel time betweena location of the first sensor and a location of the second sensor.

In another aspect, a computer-implemented method of monitoring movementof a mobile device includes initiating, in a sensor, an inquiry scanaccording to a Bluetooth standard, receiving, in the sensor, an inquiryresponse according to a Bluetooth standard from the mobile device,storing a media access control address of the mobile device contained inthe inquiry response, storing identification information of the sensor,and associating the media access control address of the mobile devicewith the identification information of the sensor to monitor movement ofthe mobile device.

In another aspect, a computer-implemented method of monitoring vehicletraffic along a roadway comprises initiating, in a sensor disposed alonga roadway, a first inquiry scan according to a Bluetooth standard,receiving, in the sensor and at a first time, a first inquiry responseaccording to a Bluetooth standard from a mobile device, the firstinquiry response including a device identifier that identifies themobile device, storing, in the sensor, the device identifier received inthe first inquiry response, storing, in the sensor, a sensor identifierthat identifies the sensor, associating the device identifier with thesensor identifier and a first time stamp that reflects the first time,initiating, in the sensor, a second inquiry scan according to aBluetooth standard, receiving, in the sensor and at a second time, asecond inquiry response according to a Bluetooth standard from themobile device, the second inquiry response including the deviceidentifier, storing, in the sensor, the device identifier received inthe second inquiry response, associating the device identifier with thesensor identifier and a second time stamp that reflects the second time,identifying that the device identifier is associated with the sensoridentifier at the first time and is associated with the sensoridentifier at the second time, and, based on having identified thatdevice identifier is associated with the sensor identifier at the firsttime as well as at the second time, deriving at least one vehicletraffic statistic based on the first time stamp and the second timestamp.

Other features also will be apparent from the description and drawings,and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a block diagram of an exemplary traffic monitoringsystem.

FIGS. 2 and 3 are flow charts illustrating exemplary processes forcollecting traffic data.

FIG. 4 is a flow chart illustrating an exemplary process for monitoringtraffic.

FIGS. 5 and 6 are block diagrams of an exemplary sensor for collectingtraffic data.

FIG. 7 is a schematic of an exemplary computer system configured toperform one or more of the processes described with respect to FIGS.2-4, based on information received through a sensor such as illustratedin FIGS. 5 and 6.

Like reference symbols in the various figures generally indicate likeelements.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary system 100 for monitoring vehicletraffic. The system 100 includes two sensors 110, 120 that are installedalong a roadway R, and a traffic monitor 130 in temporary or permanentcommunication with each of the two sensors 110, 120. Each of the sensors110, 120 and the traffic monitor may include one or more of computer700, as illustrated in FIG. 7, including a processor module 710, astorage module 720, a memory module 730, and an input/output (I/O)module 740, all connected by a system bus 760. The computer 700 includesvarious input/output devices 750.

For example, the sensors 110, 120 may be configured as unit 500 havingcharacteristics such as those illustrated in FIGS. 5 and 6. Morespecifically, the unit 500 includes a housing 501 in which variouscomponents are mounted. The unit 500 further includes the computer 700,including the storage module 720, mounted inside a computer case 510.The computer 700 is operable with a Bluetooth radio module 520 tocommunicate with discoverable Bluetooth devices, as discussed below. Thecomputer is further operable with a GPS module 530 and GPS antenna 531to obtain, for example, time and/or location information. The computer700, the Bluetooth radio module 520, and the GPS module 530 are allpowered by a battery 540. The computer 700 includes a computer programproduct stored on a computer readable medium operable to monitordiscoverable Bluetooth devices, for example, by performing the processesdescribed below.

As a vehicle V1 travels in the direction of arrow A along the roadway R,it passes within a first area 115 sufficiently proximate to the firstsensor 110 that the first sensor 110 is able to detect the presence of aBluetooth device onboard the vehicle V1. The first area 115 may beapproximately equal to a communication range of the Bluetooth radiomodule 520, and a precise location L1 of the first sensor 110 may beattributed to all places within the first area 115. While the first area115 and the second area 125 are illustrated as round in shape,associated with an omni-directional antenna, the first area 115 and/orthe second area 125 may have other shapes, such as those associated witha vagi, or other directional, antenna. Accordingly, if desired, thefirst area 115 and/or the second area 125 may be configured to coveronly portion of the roadway R, such as the lanes of a selected directionof travel, or a selected one of multiple lanes of common traveldirection. For example the first area 115 and/or the second area 125 maybe limited to lanes restricted to high occupancy vehicles, if desired.Conversely, the first area 115 and/or the second area 125 may beconfigured so as to cover all lanes at an intersection or highwayinterchange, including exit and entrance ramps, if desired.Additionally, the sensors 110 and 120 are installed such that the firstarea 115 and the second area 125 do not overlap. Thus, where the sensors110 and 120 include Bluetooth radio modules 520 having a class 1Bluetooth radio, the first and second locations L1 and L2 are selectedat a sufficient distance to reduce the possibility that a discoverableBluetooth device could receive a communication from each of the sensors110 and 120 at the same time, for example a distance more than one mile.Such spacing of the sensors 110 and 120 may additionally serve to reducethe effect of the uncertainty associated with attribution of the firstlocation L1 to all locations within the first area 115, and attributionof the second location L2 to all locations within the second area 125.

The first sensor 110 collects an identifier DID1 of a discoverableBluetooth device D1 in the vehicle V1 as the vehicle V1 drives along theroadway R through the first area 115 at a first time T1. The firstsensor stores the identifier of Bluetooth device DID1 on a storagemedium 111 along with other information, including an indication of thefirst time Ti. Subsequently, at a second time T4, after traveling alongthe roadway R, the vehicle V1 passes through the second area 125sufficiently proximate to the second sensor 120 that the second sensor120 is able to detect the presence of the Bluetooth device onboard thevehicle V1. The second sensor 120 collects the identifier DID1 of theBluetooth device D1 and stores the identifier DID1 of Bluetooth deviceD1 on a storage medium 121 along with other information, including thesecond time T4. The first sensor 110 and the second sensor 120 eachcollects and stores identifiers for multiple discoverable Bluetoothdevices of multiple vehicles as they pass the sensors 110, 120. Themultiple discoverable Bluetooth devices may be detected, and theidentifiers collected and stored, in a single scan, in multiple scansperformed at multiple times, or both.

The device identifier DID1 identifies the Bluetooth device D1, andallows a determination that the same vehicle, such as vehicle V1,traveled past both the first sensor 110 and the second sensor 120. It isnot necessary, however, that the device identifier DID1 containinformation that identifies the vehicle V1 itself, or of an owner oroperator of vehicle V1. For example, the device identifier DID1 may be aMAC address of the Bluetooth device, with no indication of how thatdevice identifier of MAC address relates to the vehicle orowner/operator thereof For example, a MAC address of a Bluetooth deviceis sufficient to enable reliable identification of the Bluetooth deviceD1, but without more is not sufficient to track an individual using theMAC address of a Bluetooth device, the privacy of individuals whoseBluetooth device MAC address is collected is not at risk. To furtheraddress privacy concerns, only a portion of the MAC address may be usedas the identifier, or the identifier may be derived from the MACaddress, such that even the complete MAC address is not stored. Thus,even if it becomes possible to track an individual using a Bluetoothdevice MAC address, the system 100 may protect the privacy ofindividuals from whom or with respect to which it collects deviceidentifiers.

As illustrated, the first sensor 110 collects and stores the identifierDID1 of the device D1 at time T1. Additionally, the first sensor 110stores an indication L1 of the location of the first sensor 110 and anindication (scan 1) of the scan in which the identifier DID1 of thedevice D1 was collected. The first sensor 110 also collects and storesidentifiers DID2, DID3 of other discoverable Bluetooth devices that passthe first sensor 110. As illustrated, the identifier DID2 is collectedat a time T2 in scan 2, and DID3 is collected at a time T3 in scan 3.All three identifiers DID1, DID2, and DID3 are attributed with thelocation L1. Additionally, the first sensor 110 may store its ownidentifier SID1. Similarly, the second sensor 120 collects and storesidentifiers and other information on the storage medium 121. Forexample, the second sensor 120 collects and stores the identifier DID1of the device D1 of the vehicle V1 at a time T4. The second sensor 120also stores the number of the scan in which the identifier DID1 wascollected and an indication L2 of the location of the second sensor 120.The identifiers DID2 and DID3 were collected from discoverable Bluetoothdevices at times T5 and T6, and in scans 2 and 3, respectively, of thesecond sensor 120. The second sensor 120 also stores its own identifierSID2.

While the sensors 110 and 120 are shown collecting the same set ofidentifiers DID1-DID3, each sensor 110, 120 may additionally collect andstore identifiers and other information for any discoverable Bluetoothdevices that enter areas 115 and 125, respectively. This is true whetheror not another one of the sensors collects and stores, or fails tocollect and store, an identifier and other information associated withsuch discoverable Bluetooth devices. This failure may be due, forexample, to a vehicle exiting the roadway at a location after the firstsensor 110 and before the second sensor 120, turning around beforereaching the second sensor, stopping before reaching the second sensor,or a simple failure of the sensor to collect an identifier of a deviceas it passes the sensor.

The sensors 110, 120 communicate the collected identifiers and theadditional information to the traffic monitor 130. The traffic monitor130 analyzes the collected identifiers and other information todetermine traffic statistics for vehicles having an onboard discoverableBluetooth device for which an identifier was collected at both of thesensors 110, 120. For example, the traffic monitor 130 may generate,store, and/or display a travel time for the vehicle V1 to travel fromthe first area 115 proximate the first sensor 110 to the second area 125proximate the second sensor 120 by taking the difference of time T4 whenthe identifier DID1 was collected at the second sensor 120 and the timeT1 when the identifier DID1 was collected at the first sensor 110.Additionally, an average speed for the vehicle V1, at least duringtravel from the first area 115 proximate the first sensor 110 to thesecond area 125 proximate the second sensor 120, is calculated bydividing the travel time of the vehicle V1 between the first and secondareas 115 and 125, represented by the difference between the time T4 andthe time Ti, by a distance between the first location L1 and the secondlocation L2. The distance between the first location L1 and L2 may bedetermined and provided to the traffic monitor for this purpose. Forexample, the route distance may be measured empirically, or it may beestimated based on a comparison of location coordinates provided by theGPS module 530.

Additionally, the traffic monitor 130 may analyze the collectedinformation to determine traffic statistics for vehicles carrying adiscoverable Bluetooth device for which an identifier was collected atonly a single sensor. For example, vehicle traffic flow volume may bedetermined by analysis of a sum of the number of different discoverableBluetooth devices for which an identifier was collected. As anotherexample, if a vehicle is stopped or moving slowly, an identifier of adevice in the vehicle may be collected and stored in multiple scans overa period of time. This may occur, for example, when the vehicle ismoving slowly and, thus, remains within communication range of a singlesensor for a relatively long period of time, or when the vehicle isstopped, such as at a traffic light. A residence time, or time that avehicle remained within range of the sensor, may be determined by thedifference between the first and last times the identificationinformation is collected from a discoverable Bluetooth device associatedwith the vehicle. As another example, a speed of the vehicle may bedetermined by dividing the residence time into a distance associatedwith the communication range of the sensor.

FIG. 2 is a flow chart illustrating an exemplary process for collectingtraffic data.

Specifically, the sensors 110, 120 perform a data collection process 200to collect the identifier of one or more discoverable Bluetooth device.The sensors 110, 120, begin (201) when a command is provided by a user,such as by initiating a computer program product stored on a computerreadable medium, such as the storage module 720, operable to execute theprocess 200. Alternatively, the sensors 110, 120, may be configured tobegin (201) automatically when the sensors 110, 120 are powered on andan operating system of the computer 700 is initialized. Once begun, thesensors 110, 120 then perform a scan routine (203) to collectidentification information from discoverable Bluetooth devices withinthe first area 115 and within the second area 125, respectively.Accordingly, the scan routine is performed according to a Bluetoothstandard. For example, the device inquiry routine of the

Bluetooth generic access profile may be used to scan (203) fordiscoverable Bluetooth devices. Thus, the scan (203) includestransmitting multiple generic inquiry requests according to a Bluetoothstandard via an I/O device 750 in the form of the Bluetooth radio module520. While the scan routine is performed according to a Bluetoothstandard, the sensors need not, necessarily, perform additionalprocesses otherwise contemplated by the

Bluetooth standard. For example, the sensors do not necessarily proceedto perform a name discovery routine.

In response to a scan (203), the sensors 110, 120 may receive one ormore response (205) from a discoverable Bluetooth device that receivedthe inquiry request of the scan (203). Each response includes, amongother things, a device identifier in the form of a MAC address. Thesensors 110, 120 store a device identifier identifying the Bluetoothdevice sending the response. as the device identifier may be the deviceMAC address received in the responses (207), a portion of the MACaddress, or an identifier derived from the MAC address, such as a valuethat is the result of a transform applied to the MAC address. The MACaddresses, or other identifiers, may be stored as the identifier of theresponding Bluetooth device. The device identifier may be stored on thestorage module 720, on the memory module 730, or on an I/O device 750configured as a storage or memory device and connected to the I/O module740. The process 200 then continues to scan for discoverable Bluetoothdevices (203). Other information of the Bluetooth device included in theresponses, such as clock information and page scan type information, maybe ignored or discarded, if desired. Alternatively, this additionalinformation included in the response (205) may be used with the MACaddress to create another arbitrary identifier. Similarly, less than allof the MAC address, or some other value derived from at least a portionof the MAC address, may be used as the identifier, and stored by thesensor receiving the response.

Optionally, when the data collection process begins (201), an electroniclog file may be created or accessed on the storage module 720, memorymodule 730, or on an I/O device 750 configured as a storage or memorydevice. A sensor identifier SID1 that identifies the first sensor 110,for example, is stored in the log file as an indication that the logfile was created by or on the first sensor 110, and as an indicationthat any device identifiers stored in the log file were collected by thefirst sensor 110 and at the first location L1 of the first sensor. Thesensor identifier SID1 may be the Bluetooth MAC address of the sensor110 creating the log file. Alternatively, the sensor identifier SID1 maybe only a portion of the MAC address of the sensor 110, a derivative ofthe MAC address of the sensor 110, or any other value, including anarbitrary value.

Other information may also be stored in the log file when the datacollection process begins. For example, an indication L1 of the locationof the sensor 110, and an indication TO of the time and date when theprocess 200 began (201) may be stored in the log file. The locationindicated by the indication L1 and the time and date indicated by theindication TO may be obtained by an I/O device formed as the GPS module530, and may additionally be used to set the system clock of the sensor110. Furthermore, in addition to storing the device identifiers of theBluetooth devices sending a response (205), the sensors 110, 120 maystore in the log file an indication of the date and time that theresponse was received (205), such as the date and time indicated by thesystem clock. Finally, the sensors 110, 120 may store in the log fileinformation indicating the number of the scan for which the response wasreceived. Thus, each device identifier may be associated in the log filewith various additional pieces of information, that indicate that theparticular Bluetooth device identified by the device identifier waslocated at the location indicated at the time and date indicated.

Referring more specifically to the scan (203) and receiving responses(205) performed by the sensors 110, 120, in order to locate discoverableBluetooth devices, the sensors 110, 120 must scan multiple channelsemployed in the Bluetooth protocol. A typical Bluetooth inquiry scan cantake 5 seconds or more to complete the process of transmitting aninquiry request and receiving responses on all 32 communication channelsreserved for such requests. While this may be acceptable for slow-movingtraffic, such as pedestrian traffic, vehicle traffic may not be withinrange of the sensor for long enough to be detected by the typicalBluetooth inquiry scan. Thus, the specific scan routine (203) performedby a sensor may determine whether the desired information is collected,and whether the information is collected reliably and/or efficiently.For example, a discoverable Bluetooth device D1 within a vehicle V1traveling at highway speeds, such as speeds greater than fifty miles perhour (50 mph) may be in range of a sensor 110, 120 for less than a fewseconds. In order for the identifier DID1 of the discoverable Bluetoothdevice D1 to be collected by the sensors 110, 120 in such anenvironment, the scan (203) may need to be configured to collect theidentifier DID1 in less time, i.e., within a time period in which thedevice D1 is within communication range of the sensors 110, 120. Thescan (203) may be configured by determining, for example, a maximumnumber of responses to receive (205), a maximum time to scan (203), amaximum number of scan routines (203) to perform, or other scanparameter. An exemplary process configured by determining a maximumnumber of responses to receive and a maximum time to scan is illustratedin FIG. 3.

FIG. 3 is a flowchart illustrating an exemplary process 300 forcollecting Bluetooth device identifiers in which a threshold number ofresponses and a threshold scan time have been determined. The process300 begins (301) when the sensor is activated, and, as with process 200described above, a log file may be created and/or accessed on a storagemedium of the sensor and a location indication, a time indication, and asensor identifier may be stored in the log file. The sensor theninitiates a scan (303), which includes an interlaced Bluetooth generalinquiry scan routine having a duration of approximately 1.28 seconds.The interlaced Bluetooth general inquiry scan routine transmits aninquiry request and listens for responses on all 32 channels in apseudo-random pattern within the approximately 1.28 second duration.After initiating the scan (303), a determination is made as to whether aresponse has been received (305). If a response has been received, thena device identifier is stored in the log file (307) along with the time,date, location, and the number of the scan, as discussed above. Afterlogging the device identifier and other information (307), adetermination is made as to whether a number of responses received isgreater than, or equal to, a threshold number. If the determination ismade that the number of responses received is greater than, or equal to,the threshold number of responses (309), then the scan may terminate andthe process 300 may initiate a new scan (303).

The threshold number may be user-defined to achieve a desired scanningcharacteristic. For example, the lower the threshold number, the soonerthe scan terminates and the process 300 will initiate a new scan 303.This may result in more frequent scans, and a greater opportunity tocollect the same identifier from the same device multiple times at thesame sensor. Conversely, as the threshold number increases, it becomesless likely that the scan will terminate due to receiving the thresholdnumber of responses. This may allow for the scan to continue for agreater duration, and start a new scan (303) less frequently. The longerscans may have less likelihood of collecting the same identifier from adevice multiple times.

If, instead, the determination is made that the received number ofresponses is less than the threshold number (309), or if thedetermination is made that no response has been received (305), then thedetermination is made as to whether the scan time, i.e., the duration ofthe scan, is greater than, or equal to, a threshold time (311). If thescan time is less than the threshold time, then the process returns tomake another determination whether a response has been received (305).If, instead, the scan time is greater than, or equal to, the thresholdtime, which indicates that the scan duration has met or exceeded adesired maximum time, then the process 300 may terminate the scan andproceed to initiate a new scan (303).

The threshold time may be selected as a number sufficient to allow forcompletion of an integer number of the approximately 1.28 secondduration interlaced general inquiry scan routine, assuming that the scanis not terminated sooner by making the determination that the thresholdnumber of responses has been reached. Accordingly, instead of making adetermination as to whether the scan time is greater than or equal to athreshold time (311), the process 300 may alternatively, oradditionally, make a determination as to whether a threshold number ofscan routines have been completed. As with the threshold number ofresponses, the threshold time (or number of scan routines) may beselected to achieve a desired scanning characteristic. For example, ahigher threshold time will result in longer scan duration, which mayreduce the number of redundant device identifiers collected at a givensensor.

FIG. 4 is a flow chart illustrating a process 400 for determining one ormore traffic statistic. The process 400 includes scanning, at multiplesensors, for discoverable Bluetooth devices (411, 421, 431). If anyidentifiers of Bluetooth devices are received during the scan (411, 421,431), the device identifiers, such as the MAC addresses of respondingBluetooth devices, are stored on a computer readable medium (413, 423,433). The device identifiers collected by the sensors are alsoassociated with a sensor identifier (415, 425, 435). The association(415) may be performed by storing each device identifier in a log filecontaining an identifier identifying the sensor that collected thedevice identifier. The process 400 further includes reporting thecollected device identifiers to a traffic monitor (417, 427, 437). Suchreporting (417, 427, 437) may be performed, for example, automaticallyon a periodic basis, on a continual basis, or a single time, such aswhen the sensor has completed collecting device identifiers. Asillustrated in FIG. 4, the first sensor 110 and the second sensor 120,for example, may perform the scan for devices (411, 421), loggingreceived device identifiers (413, 423), associating the deviceidentifiers with the identifier SID1, SID2 identifying the sensor 110,120 (415, 425), and reporting to the traffic monitor 130 (417, 427).

The traffic monitor 130 receives the data reported from the sensors(441), including the collected device identifiers associated with theidentifier identifying the sensor that collected the device identifier.The traffic monitor 130 also receives additional information stored bythe sensors, including, for example, the time and date that the deviceidentifier was collected and the location of the sensor when the deviceidentifier was collected. The traffic monitor 130 may analyze the datareceived from the sensors 110, 120 to identify device identifiers thatwere collected in association with two or more sensors (443). Thetraffic monitor may then determine traffic statistics based on theassociation of a device identifier with two or more sensors (445).Additionally, the determination of the traffic statistics may be made(445) based on the additional information stored by the sensors andreported to the traffic monitor 130.

For example, the determination (445) may be made, based on theassociation of a device identifier with two sensor identifiers, that thevehicle carrying the device traveled along a route between the locationsof the two sensors identified by the sensor identifiers. Furthermore, iftime information was also stored by the sensors, the traffic monitor 130may determine (445) a time of travel for the vehicle between thelocations of the sensors by determining the difference between the timesthe device identifier was collected at the two sensors. Additionally, iflocation information was stored by the sensors, the traffic monitor 130may determine (445) a speed of travel for the vehicle between thelocations of the sensors by dividing the time of travel between thesensors into the route distance between the locations of the sensors.

In an exemplary use, data collection is performed for vehicles travelingon a section of freeway. Portable sensors are located approximately 1.2miles apart along the route of the freeway, where each is installed atthe gore of an off-ramp at two successive interchanges on the freeway.Each Bluetooth sensor includes a class one Bluetooth transceiver, acentral processing unit, a micro SD card for non-volatile memory, and aGPS receiver. Each sensor is powered through a 12-volt battery andhoused in a weather-proof non-metallic container. The sensors arepositioned near a guard rail post near each off-ramp, and secured inplace with a lock and cable.

Each sensor is powered on by a technician operating a switch. Onpower-up, each sensor automatically performs a power-on test sequenceduring which each sub-system is checked for faults. After the power-ontest sequence, the GPS receiver is automatically activated and thesystem waits until a valid GPS location solution is returned from theGPS receiver. The GPS receiver returns a standard NEMA coded messagestream containing the geodetic coordinates of the sensor, includinglatitude, longitude, elevation, and time reference information. Thesevalues are automatically stored in a local data file on the Micro-SDcard. Upon receiving a valid reference time from the GPS sub-system, thecentral processing unit system clock is automatically initialized basedon the time reference information, and the sensor automatically enters adata collection mode.

During the data collection mode, each sensor is configured toperiodically initiate a

Bluetooth inquiry scan request in an interlaced mode. A completeinterlaced inquiry scan routine takes approximately 1.28 seconds. Duringeach scan, a unit alternatingly transmits an inquiry request on 32Bluetooth channels and listens for inquiry responses in pairs, and in apseudo random order. For example, for a complete interlaced inquiry scanroutine, a sensor may transmit an inquiry request on a first channel ofthe 32 channels, transmit an inquiry request on a second channel of the32 channels, listen for responses on the first channel, then listen forresponses on the second channel. The sensor repeats this pattern untilall 32 channels have been scanned, again, in pseudo random order. Itshould be understood that the Bluetooth standard involves frequencyhopping, where each channel comprises a predetermined pattern offrequency hops. Each Bluetooth inquiry scan comprises, for example, 4complete interlaced inquiry scan routines and takes approximately 5.12seconds to complete. A maximum threshold time is set for the Bluetoothinquiry scans at approximately 5.25 seconds, and each sensor isconfigured to initiate a new Bluetooth inquiry scan if the thresholdtime is reached. The approximately 5.25 second threshold time allows,for example, some delay between terminating one complete interlacedinquiry scan routine and initiating a subsequent complete interlacedBluetooth inquiry scan routine, some delay after terminating the fourthcomplete Bluetooth interlaced scan routine and initiating a subsequentBluetooth inquiry scan, and/or some other additional feature, such as,for example, an error check.

Specifically, in one example, one Bluetooth inquiry scan is initiatedand no responses are received within an approximately 5.25 second periodof time from the initiation thereof, then the Bluetooth inquiry scan isterminated, and a subsequent Bluetooth inquiry scan is initiated.Alternatively, however, an indication that no responses were received inresponse to the Bluetooth inquiry scan may be stored in a data filelabeled with the Bluetooth MAC address of the sensor. The indication,such as a MAC address of 00:00:00:00:00, is and appended with adate-time stamp indicating the approximate time of initiation of the

Bluetooth inquiry scan for which a response was received. The datastorage is enforced at the end of each Bluetooth inquiry scan in which aresponse is received.

After another Bluetooth inquiry scan is initiated, two responses arereceived within an approximately 5.25 second period of time from theinitiation of the subsequent Bluetooth inquiry scan, after which thesubsequent Bluetooth inquiry scan is terminated, and another subsequentBluetooth inquiry scan is initiated. For each Bluetooth responsereceived, the sensor records on the micro SD card of the sensor the MACaddress of the responding unit and an indication of the date and timewhen the response was received. Other information recorded in the datafile on the micro SD card includes the scan number, and the duration ofthe scan from which the response was received. This data is stored inthe data file labeled with the Bluetooth MAC address of the sensor, andthe data storage is enforced at the end of each Bluetooth inquiry scanin which a response is received.

After yet another Bluetooth inquiry scan is initiated, four responsesare received within approximately 3.5 seconds, and the Bluetooth inquiryscan is terminated before reaching an approximately 5.25 second periodof time. Information from each of the four responses is stored asdescribed above in the data file on the micro SD card of the sensor thatreceived the responses. A subsequent Bluetooth inquiry scan is theninitiated, and the sensor automatically continues operating in this wayuntil the battery is unable to supply adequate power for normaloperation, or until the scanning is terminated by a technician. If thesensor ceases operation due to inadequate battery power, little or nodata is lost due to the enforcement of the data storage after eachBluetooth inquiry scan.

The battery capacity allows for continuous unattended operation of eachsensor for up approximately six days. After six days of operation, thesensors are retrieved from the field. The micro SD card from each sensoris removed and the data from each micro SD card are transferred to acentral computer for processing. Each micro SD card contains three filesfor each period of data collection operation. The three files are thedata file including information obtained from the Bluetooth responsesrecorded by the sensor, a GPS file including the geodetic informationreported by the GPS receiver, and an info file including versioning andother information about each sensor. Each file is named using the MACaddress of the sensor, and a date-time stamp that indicates anapproximate time that scanning begins and that is based on the timereference information from the GPS receiver. The files are appended,respectively, with either ‘data’, ‘gps’ or ‘info’ to indicate the typeof information included in the file. At the central computer, theBluetooth data collected on the freeway is processed and correlated toobtain valid traffic information. The central computer is a Windowsplatform machine running custom software configured to read and processthe data. The processing is accomplished in three phases or steps.

In the first step, data from each sensor is read into the computer andis processed to obtain detection records. A detection record representsone instance of a vehicle passing a sensor. A single vehicle containinga mobile Bluetooth device may have a response recorded more than onetime as it enters, passes through, and/or exits the sensor's detectionarea. The lower the speed of the vehicle, the higher the probability isof detecting the vehicle more than once. To obtain the detectionrecords, each recorded Bluetooth response is examined to determinewhether any other recorded Bluetooth response with the same device MACaddress has been recorded within two minutes before or after the time ofthe recorded Bluetooth response. All recorded Bluetooth responses withthe same device MAC address that are separated by less than two minutesare combined into a single detection record. The detection recordincludes the device MAC address, the number of recorded Bluetoothresponses that contained the device MAC address, the date and time ofthe first recorded response that contained the device MAC address andthat was part of the detection record, and the date and time of the lastrecorded response that contained the device MAC address and that waspart of the detection record. A time value equal to a median of the dateand time of the first recorded response and the date and time of thesecond recorded response is attributed to the detection record as theapproximate date and time of the time record.

Next, the GPS data file is read, and the latitude and longitude valuesstored by each sensor are recorded. The distance between sensors iscomputed based on great-circle distances. Additionally, a user isprompted to manually enter a value of the route distance between the twosensors, which value replaces the great-circle distance. Thegreat-circle distance is used if the distance is unknown or if a valueis not entered by the user for another reason.

Next, the computer identifies detection records of different sensorsthat contain the same device MAC address. Specifically, for eachdetection record, the detection records are searched to identifydetection records that contain the same device MAC address and that havea time value within 30 minutes of a time value of the detection record.If a detection record having a matching device MAC address isidentified, a paired detection record is created that links thedetection records having the same device MAC address. A paired detectionrecord consists of the device MAC address, the time value of one of thedetection records, the time value of the other detection record, and thedifference between the two time values, which is a measure of thepassage time between the one detection record and the other detectionrecord. All detection records are processed in this manner. If two ormore detection records having a matching device MAC address areidentified within a 30 minute period, the earliest record is used tocreate a paired detection record.

Next, paired detection records are filtered for outliers. Specifically,paired detection records are sorted by the time value of the firstdetection record. For a given paired detection record, all the paireddetection records, but not more than the 15 nearest paired detectionrecords having a time value before, and all, but not more than the 15nearest paired detection records having a time value after the givenpaired detection record, are used to determine the difference betweenthe 75th and 25th percentile of passage times. This measure, referred toas the interquartile range, forms the basis for the filter. If thepassage time of the given paired detection record falls outside theboundary defined by plus or minus three inter-quartile ranges from themedian passage time of the paired detection records (e.g., 31 paireddetection records), then it is considered an outlier and omitted fromany further processing. All paired detection records are filtered inthis manner. The mean and standard deviation of passage times are thendetermined for successive five-minute increment periods. Mean andstandard deviation of speed are similarly calculated by dividing thedistance value between the sensors by the corresponding travel times.

A number of exemplary implementations have been described. Nevertheless,it will be understood that various modifications may be made withoutdeparting from the spirit and scope of the technology discussed herein.For example, the system 100 may be configured differently from theconfigurations described and illustrated above. In anotherconfiguration, the traffic monitor 130 may be eliminated and thefunctions and features associated therewith may instead be included insensor the first sensor 110, the second sensor 120, or another device.Similarly, in another configuration, two or more sensors 110 may beinstalled approximately at the first location L1, and responses havingduplicate device identifiers DID1 and recorded within a selected amountof time of one another may be combined in a single detection record.Additionally, the processes described above, and those claimed below,may be performed by sensor devices having a different configuration,including hardware and/or software, than those described above.Likewise, the devices and systems described above may be used inprocesses different from those described above and claimed below. Forexample, the systems and devices may be used to monitor pedestriantraffic, inventory traffic, or movement of other item.

In another embodiment, the devices also could be permanently mounted forcontinuous reporting, or quickly deployed for surveys or events.Wireless data networking (or land-line links if permanently installed)options could be used to transmit the records to a database forreal-time monitoring. If real-time monitoring is not a concern, the datarecords could simply be stored locally and downloaded periodically asconvenient. Matching of the unique Bluetooth address and related traveltime and OD analysis would be performed at the database.

The Bluetooth Traffic Monitoring Concept can be extended to includevolume estimates as follows. Bluetooth capable devices are positioned onall legs of an intersection. By logging and matching public network ID'sof the devices in the traffic stream, an estimate of the volume oftraffic and the turning movement proportions (number of vehicles goingstraight, turning left, and turning right) are obtained. Volumeestimates can be obtained with a single Bluetooth device, withoutacquiring matching pairs from two such devices. Such information isvaluable in assessing signal timing. The same concept can be used toestimate throughput volume, routing, and turning movement logistics onany type of transportation network facility, be it roads, transit, orpedestrian movement.

What is claimed is:
 1. A computer-implemented method of monitoringvehicle traffic along a roadway comprising: initiating, in a firstsensor disposed at a first location along a roadway, a first inquiryscan according to a Bluetooth standard; receiving, in the first sensorand at a first time, a first inquiry response according to a Bluetoothstandard from a mobile device, the first inquiry response including amedia access control address of the mobile device; storing, in the firstsensor, a first device identifier identifying the mobile device based onthe first inquiry response; storing, in the first sensor, a first sensoridentifier that identifies the first sensor; associating the firstdevice identifier with the first sensor identifier and a first timestamp that reflects the first time; initiating, in a second sensor, asecond inquiry scan according to a Bluetooth standard, wherein thesecond sensor is disposed at a second location along a roadway;receiving, in the second sensor and at a second time, a second inquiryresponse according to a Bluetooth standard from the mobile device, thesecond inquiry response including the media access control address ofthe mobile device; storing, in the second sensor, the first deviceidentifier identifying the mobile device based on the second inquiryresponse; storing, in the second sensor, a second sensor identifier thatidentifies the second sensor; associating the first device identifierwith the second sensor identifier and a second time stamp that reflectsthe second time; identifying that the first device identifier isassociated with the first sensor identifier and with the second sensoridentifier; and based on having identified that the first deviceidentifier is associated with the first sensor identifier and the firsttime stamp as well as with the second sensor identifier and the secondtime stamp, deriving at least one vehicle traffic statistic based on thefirst time stamp, the second time stamp, the first location, and thesecond location.